Cell Mediated and Humoral Immune Response in Chickens Infected with Avian Infectious Bronchitis

Abstract

A lymphocyte transformation (LT) microassay was developed to study cell-mediated immune (CMI) responses in chickens infected with avian infectious bronchitis virus (IBV). Peripheral blood lymphocytes, from chickens inoculated with IBV strain Massachusetts-41 (M-41) and uninoculated control birds, were incubated with homologous antigen and the mitogen phytohaemagglutinin (PHA). The degree of lymphocyte transformation was determined by measuring the incorporation of ( 3 H)-thymidine. Humoral immunity was monitored for comparison using the haemagglutination inhibition (HI) microassay. LT and HI tests were performed during the week prior to inoculation and at weekly intervals for six weeks after inoculation. Lymphocytes from inoculated birds showed significant increases in blastogenesis, as compared to control birds, following antigen and mitogen stimulation. Positive stimulation indexes (Si’s) with IBV antigen were observed in 94% of inoculated birds at five days, in 100% at 12 days and then the proportion of positives fell to 6% at 40 days after inoculation. Positive HI titres appeared one week later than positive Si’s with IBV antigen and were demonstrated in 100% of the birds from the 12th to 40th day after inoculation. Although SI’s and HI titres both peaked at 12 days, there was no evidence of a direct correlation between CMI and antibody production